to make the BOPTools available in python3 the way to import these tools had to be changed:
old: ```from Part import BOPTools``` -> new: ```import BOPTools```
this is also changed for python2
* display originals in tree under the features (like Part Fuse does)
* unhide originals upon delete
* display message box when computing the feature fails on creation
Attributions:
Mark (quick61) - icons
Yorik - help with internationalization
Everyone who appeared in forum thread "A new Part tool is being born...
JoinFeatures!" - for endorsement!
http://forum.freecadweb.org/viewtopic.php?f=22&t=11112
